1. Field of the Invention
The present invention relates to communication apparatuses, such as mobile communication apparatuses, and to antenna structures included in such apparatuses.
2. Description of the Related Art
One type of small antenna provided in mobile communication apparatuses, such as mobile telephones and GPS (Global Positioning System) apparatuses, is a surface-mounted antenna that is produced by forming a radiating electrode on a dielectric or magnetic base member. The radio-wave transmission/reception frequency of the surface-mounted antenna, that is, the resonant frequency of the radiating electrode, is determined by the complex relationship among various factors including the size of the base member, the dielectric constant of the base member when the base member is made of dielectric material, and the size and the shape of the radiating electrode.
When changing the radio-wave transmission/reception frequency of the surface-mounted antenna, that is, when changing the resonant frequency of the radiating electrode, a great amount of time and labor is required to design the surface-mounted antenna. As a result, the cost of the surface-mounted antenna increases.
An antenna structure 1 such as that shown in FIG. 10A is proposed. The antenna structure 1 contains a surface-mounted antenna 2, a board-side control electrode 4 disposed on a mounting board 3 (a circuit board of a communication apparatus), a switch circuit 5, and a ground conductor 6. The surface-mounted antenna 2 is a xcex/4 transmission line type and is formed by a dielectric or magnetic base member 7, a radiating electrode 8, a ground electrode 9, a feeding electrode 10, and an antenna-side control electrode 11.
In the surface-mounted antenna 2, the ground electrode 9 is disposed on a bottom surface 7b of the base member 7, and the radiating electrode 8 is arranged to extend from a side surface 7f to a top surface 7a. A first end of the radiating electrode 8 communicates and connects with the ground electrode 9, thus defining a ground end. A second end of the radiating electrode 8 defines an open end 8a. A portion of the open end 8a extends from the top surface 7a to the side surface 7d of the base member 7.
A first end of the antenna-side control electrode 11 opposes the extended portion of the open end 8a with a gap therebetween. A capacitance is generated between the open end 8a of the radiating electrode 8 and the antenna-side control electrode 11. A second end of the antenna-side control electrode 11 is arranged such that it wraps around the side surface 7d to the bottom surface 7b of the base member 7. The second end of the antenna-side control electrode 11 opposes the ground electrode 9 with a gap therebetween. The antenna-side control electrode 11 electrically floats.
The feeding electrode 10 is arranged to extend from the bottom surface 7b through the side surface 7d to the top surface 7a of the base member 7. A top end of the feeding electrode 10 opposes the open end 8a of the radiating electrode 8 with a gap therebetween. A second end of the feeding electrode 10 opposes the ground electrode 9 with a gap therebetween.
On the mounting board 3, a region in which the surface-mounted antenna 2 is mounted is a groundless portion in which the ground conductor 6 is not provided. The board-side control electrode 4, which electrically floats, and the switch circuit 5 are disposed on the groundless portion. A signal supply source 12 is disposed on the mounting board 3. A feeding wiring pattern 13 which is electrically connected with the signal supply source 12 is provided on the groundless portion.
In order to mount the surface-mounted antenna 2 on the mounting board 3, the surface-mounted antenna 2 is mounted on the groundless portion of the mounting board 3 so that the antenna-side control electrode 11 of the surface-mounted antenna 2 is electrically connected with the board-side control electrode 4 of the mounting board 3, so that the board-side control electrode 4 and the antenna-side control electrode 11 electrically float, and such that the feeding electrode 10 of the surface-mounted antenna 2 is electrically connected with the feeding wiring pattern 13 of the mounting board 3.
In this state, when the signal supply source 12 supplies a signal through the feeding wiring pattern 13 to the feeding electrode 10 of the surface-mounted antenna 2, the signal is transferred from the feeding electrode 10 to the radiating electrode 8 by capacitive coupling, and the radiating electrode 8 is excited. Thus, radio waves can be transmitted or received.
FIG. 10B shows an equivalent circuit diagram of the antenna structure 1. Referring to FIG. 10B, L denotes the inductance of the radiating electrode 8, R1 denotes the radiation resistance of the radiating electrode 8, R2 denotes the internal resistance of the radiating electrode 8, C1 denotes the capacitance between the open end 8a of the radiating electrode 8 and the antenna-side control electrode 11, C2 denotes the capacitance between the open end 8a of the radiating electrode 8 and the feeding electrode 10, and C3 denotes the capacitance between the radiating electrode 8 and the ground.
In the antenna structure 1, when the switch circuit 1 is switched on and when the board-side control electrode 4 is grounded through the switch circuit 5, the capacitance C1 between the open end 8a of the radiating electrode 8 and the board-side control electrode 4 influences the resonant frequency of the radiating electrode 8. In contrast, when the switch circuit 5 is switched off, the capacitance C1 does not influence the resonant frequency of the radiating electrode 8. Accordingly, the influence of the capacitance C1 on the radiating electrode 8 varies according to whether or not the switch circuit 5 is switched on or off, and hence the resonant frequency of the radiating electrode 8 varies.
In the antenna structure 1 arranged as described above, the resonant frequency of the radiating electrode 8 can be easily changed by switching the switch circuit 5 on or off without changing the size and the shape of the radiating electrode 8 of the surface-mounted antenna 2 or the size of the base member 7.
In the antenna structure 1, the structure of the switch circuit 5 is complex, and the switch circuit 5 is expensive. Thus, the antenna structure 1 is not commercially feasible.
In order to solve the foregoing problems, preferred embodiments of the present invention provide an antenna structure which has a simple configuration and which is capable of easily changing the resonant frequency of a radiating electrode without changing a surface-mounted antenna. In addition, preferred embodiments of the present invention provide a communication apparatus including such a novel antenna structure.
In order to achieve the foregoing advantages, preferred embodiments of the present invention, an antenna structure includes a surface-mounted antenna including a radiating electrode disposed on a base member, the surface-mounted antenna being a xcex/4 transmission line type, a first end of the radiating electrode being a ground end and a second end of the radiating electrode being an open end, a mounting board on which the surface-mounted antenna is mounted, an antenna-side control electrode disposed on the base member of the surface-mounted antenna, the antenna-side control electrode having a capacitance generated between itself and the open end of the radiating electrode, a ground conductor disposed on the mounting board and which functions as ground, a board-side control electrode disposed on the mounting board, which is electrically connected with the antenna-side control electrode, and which electrically floats, and a resonant frequency adjuster having at least one of an inductance and a capacitance. The board-side control electrode is electrically connected with the ground conductor through the resonant frequency adjuster.
The resonant frequency adjuster may include at least one of or a combination of at least two of a chip inductor component, a chip capacitor component, an inductor pattern, and a capacitor pattern.
According to another preferred embodiment of the present invention, an antenna structure includes a surface-mounted antenna including a radiating electrode disposed on a base member, the surface-mounted antenna being a xcex/4 transmission line type, a first end of the radiating electrode being a ground end and a second end of the radiating electrode being an open end, a mounting board, on which the surface-mounted antenna is mounted, an antenna-side control electrode disposed on the base member of the surface-mounted antenna, the antenna-side control electrode having a capacitance that is generated between itself and the open end of the radiating electrode, a ground conductor disposed on the mounting board and which functions as ground, a board-side control electrode disposed on the mounting board, which is electrically connected with the antenna-side control electrode, and which electrically floats, and a resonant frequency adjuster including a solder bridge connecting the board-side control electrode and the ground conductor or a strip line. The board-side control electrode is electrically connected with the ground conductor at high frequencies through the resonant frequency adjuster.
According to yet another preferred embodiment of the present invention, an antenna structure includes a surface-mounted antenna including a radiating electrode disposed on a base member, the surface-mounted antenna being a xcex/4 transmission line type, a first end of the radiating electrode being a ground end and a second end of the radiating electrode being an open end, a mounting board on which the surface-mounted antenna is mounted, an antenna-side control electrode disposed on the base member of the surface-mounted antenna, the antenna-side control electrode having a capacitance that is generated between itself and the open end of the radiating electrode, a ground conductor disposed on the mounting board and which functions as ground, a board-side control electrode disposed on the mounting board, which is electrically connected with the antenna-side control electrode and which electrically floats, a resonant frequency adjuster including a varicap diode, the board-side control electrode being electrically connected with the ground conductor at high frequencies through the resonant frequency adjuster, and a connection section connecting to a voltage supply source for applying a voltage to the varicap diode.
A plurality of antenna-side control electrodes may be disposed on the base member of the surface-mounted antenna. Board-side control electrodes corresponding to the antenna-side control electrodes may be disposed on the mounting board. The board-side control electrodes may be electrically connected with the ground conductor at high frequencies through separate resonant frequency adjusters.
According to a further preferred embodiment of the present invention, a communication apparatus includes an antenna structure according to preferred embodiments of the present invention described above.
According to preferred embodiments of the present invention described as above, the open end of the radiating electrode is connected at high frequencies to the ground conductor (ground) through the capacitance between the open end of the radiating electrode and the antenna-side control electrode, the antenna-side control electrode, the board-side control electrode, and the resonant frequency adjuster. The resonant frequency adjuster is preferably disposed on the mounting board. By changing the impedance between the open end of the radiating electrode and the ground using the resonant frequency adjuster, the resonant frequency of the radiating electrode can be changed. Without changing the design of the surface-mounted antenna, the resonant frequency of the radiating electrode can be easily changed by the resonant frequency adjuster. Accordingly, when the need to change the resonant frequency of the radiating electrode arises, the demand can be immediately satisfied.
The resonant frequency adjuster may be defined by and include a chip inductor component, a chip capacitor component, an inductor pattern, a capacitor pattern, a solder bridge, a strip line, a varicap diode, or other suitable element. Since the configuration of such a component is much simpler than a switch circuit illustrated in a proposed example, the antenna structure can be simplified.
According to preferred embodiments of the present invention, an antenna structure is preferably constructed by mounting a xcex/4 transmission line type surface-mounted antenna on a mounting board. The impedance between an open end of a radiating electrode and ground is changed by a resonant frequency adjuster on the mounting board, thereby changing the resonant frequency of the radiating electrode. Accordingly, the resonant frequency of the radiating electrode can be easily changed without changing the surface-mounted antenna.
When the need to change the resonant frequency of the radiating electrode arises, the need can be immediately satisfied without devoting a large amount of time and labor to design the antenna structure. An increase in cost of the antenna structure due to the design is therefore minimized, and hence the antenna can be provided at a low cost. Since the configuration of the resonant frequency adjuster can be simplified, complications in the design, manufacture and performance of the antenna structure are reliably prevented.
For these reasons, according to a communication apparatus including the antenna structure of preferred embodiments of the present invention, the cost of the communication apparatus can be reduced since the antenna structure is simple and the cost of the antenna is reduced.
A plurality of antenna-side control electrodes is disposed on the surface-mounted antenna. Board-side control electrodes corresponding to the antenna-side control electrodes are disposed on the mounting board. The board-side control electrodes are electrically connected with a ground conductor at high frequencies through separate resonant frequency adjusters. The impedance between the open end of the radiating electrode and the ground can be finely adjusted by each resonant frequency adjuster. Accordingly, it becomes even easier to adjust the resonant frequency of the radiating electrode.
Other features, elements, characteristics and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the attached drawings.